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Thread: Bad off-idle hesitation, shifting to 3rd when cruising.

  1. #1
    Trai Guest

    Default Bad off-idle hesitation, shifting to 3rd when cruising.

    The carb in question is a 670cfm Truck Avenger, it is on a mildly build Chevy 350 in my 1969 GMC 1/2 ton pickup with a TH400. From a stop in 1st gear is almost wants to die from the stumble unless i romp on the gas, once its moving there is no problem until it shifts to 3rd gear where it again stumbles a bit but after that its smooth through the RPM range, as far as i know the needles and everything is adjusted correctly and all the parts are sparkly clean and free of debris. It has a .031 Accel pump squirter running a orange pump cam, and i believe the primary and secondary jets are 68's the "dash" I.D. numbers are 90670-1 and 0535 if that helps..any suggestions would be greatly appreciated as i have racked my brain...although im no carb genious to begin with though heh.

  2. #2
    Join Date
    Dec 2009


    Before I converted to EFI, I ran a 770 CFM Truck Avenger and had to do some initial tuning. I installed a larger pump discharge nozzle (shooter), and a Holley high-flow squirter screw: I changed the front main jets down two and the rear secondary jets up four. You may need to position the accelerator pump cam in different screw hole for a longer pump shot and make sure fuel pressure is set to 5-7 psi. Also, make sure you're not exposing too much of the 'idle transfer slot' at idle (primary throttle blade adjustment). Common problem. If so, you'll need to open the secondary blades a little bit, in order to close the primary blades (without altering the idle speed). Holley has a good video pertaining to this: (Click "How To Adjust The Secondary Speed Screw") View all their carb tuning videos!
    Last edited by Danny Cabral; 04-01-2010 at 08:21 AM.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

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